1: Open Registry Editor
On Windows 2000/XP, navigate to Start, Run, then type “regedit”.
For Windows Vista, go to Start, and in the “Search” field enter “regedit”. Select it from the list that comes up or just press Enter. You may have to accept a security warning.
For Windows 7,8,8.1, press windows key and type "regedit" and hit enter.

2: Find your game in Registry Editor
For the base game only (no expansions/stuff packs/etc.) In the left pane, navigate through the folders, following this path: Computer\HKEY_LOCAL_MACHINE\SOFTWARE\EA GAMES\The Sims 2\1.0

For expansion packs/stuff packs:
In the left pane, navigate through the folders, following this path:  Computer\HKEY_LOCAL_MACHINE\SOFTWARE\EA GAMES\*name of last-installed expansion or stuff pack*\1.0


3: Change the language
1.In the right pane of the window, find the entries labeled “Language” and “LanguageName”.
2. Double-click “Language” and, using the list below, change the previous number to the number or letter corresponding to the language you wish to switch to. Be sure it’s set to “Hexadecimal”. Click OK.
3.This isn’t necessary, but it’s a good idea: Double-click “LanguageName”. Using the list below and the number or letter you just entered, enter the name of the language you wish to switch to. Click OK.
4.If you have expansion packs, especially more than one, it could be helpful to change each key for each expansion (and the base game) just to be sure they’re kept in sync. Language List
 0  English
 1   English
 2   French
 3   German
 4   Italian
 5   Spanish
 6   Swedish
 7   Finnish
 8   Dutch
 9   Danish
 10 Russian
 11 Simplified Chinese
 12 Traditional Chinese
 13 … (appears corrupted)
 14 Polish
 15 Thai
 16 Norsk (Norwegian)
 17 Portuguese
 18 Hungarian

a Portuguese
 b Czech
 c Hebrew
 d Greek
 e Japanese
 f  Korean


4: Restart the game
The change should take effect after restarting the game